X-ray imaging has been used in the medical field and for radiology in general, such as non-destructive testing and x-ray computed tomography. Conventional radiography systems use x-ray absorption to distinguish differences between different materials, such as normal and abnormal human tissues.
Conventional x-ray radiography measures the projected x-ray attenuation, or absorption, of an object. Attenuation differences within the object provide contrast of embedded features that can be displayed as an image. For example, cancerous tissues generally appear in conventional radiography because these tissues are more dense than the surrounding non-cancerous tissues. The best absorption contrast is generally obtained at x-ray energies where the absorption is high. Conventional radiography is typically performed using lower x-ray energy in higher doses to allow greater absorption and, thus, better contrast and images. In general, as the x-ray energy level increases and the x-ray dose used decreases, the quality of the conventional radiography image lessens.
Diffraction Enhanced Imaging (DEI), for example, as disclosed in U.S. Pat. No. 5,987,095, issued to Chapman et al., and U.S. Pat. No. 6,577,708, issued to Chapman et al., is an x-ray radiographic technique that derives contrast from x-ray refraction and scatter rejection (extinction) in addition to the absorption of conventional radiography. DEI can be used to detect, analyze, combine and visualize the refraction, absorption and scattering effects upon an image of an object. DEI is particularly useful for relatively thick and thus highly absorbing materials. Compared to the absorption contrast of conventional radiography, the additional contrast mechanisms, refraction and scatter, of DEI allow visualization of more features of the object.
DEI can use highly collimated x-rays prepared by x-ray diffraction from monochromator crystals. These collimated x-rays are of single x-ray energy, practically monochromatic, and are used as the x-ray beam to image an object. Once this x-ray beam passes through the object, a crystal analyzer is introduced. If the crystal analyzer is rotated about an axis, for example, the axis perpendicular to the plane shown in FIG. 1, the crystal will rotate through a Bragg condition for diffraction and the diffracted intensity will trace out a profile that is called a rocking curve. The profile will be roughly triangular and will have peak intensity close to that of the beam intensity striking the analyzer crystal. The width of the profile is typically a few microradians wide, for example 3.6 microradians within a full width of half maximum (FWHM) at 18 keV using a silicon (3, 3, 3) reflection. The character of the images obtained change depending on the setting of the analyzer crystal. To extract refraction information, the analyzer is typically set to the half intensity points on low and high angle sides of the rocking curve. At least two intensity images are obtained by a detector at different angled positions, for example, one at each of the low and high angle sides of the rocking curve, of the crystal analyzer. The intensity images are mathematically combined to obtain enhanced images, such as a refraction angle image.
Current DEI methods are typically performed using a synchrotron x-ray source and an object scanning system that moves the object through the collimated x-ray beam. There is a need for an imaging method that provides an area image without an object scanning system. There is a need for a DEI imaging method that can utilize conventional x-ray sources, and, more particularly, relatively higher x-ray tube power than generally used with conventional x-ray radiography to reduce imaging time.